1. Field of the Invention
The invention relates to a unit composed of a ball spline and a shaft with a polygonal cross section, the ball spline including an outer sleeve formed in its inner peripheral surface with ball-circulating grooves in a vertically or horizontally symmetric disposition, a pair of holders each having a vertically or horizontally symmetric structure and an angle slightly larger than an angle .alpha. when assembled in the outer sleeve, the holders holding a desired number of balls and assembled in the outer sleeve with being inflected inwardly, and a pair of holder retainers fitted to the opposite opening ends of the outer sleeve; and the shaft formed with four ball-circulating grooves in the opposite sides of its opposite two sides and inserted in the ball spline.
2. Description of the Prior Art
There are two types in normally used ball splines for different diameter spline shafts, one referred to as a casing type having balls directly assembled in a body and the other a cage type employing a holder. Cageless type ball splines are also known which eliminate the need for any cage so as to reduce the number of required parts and thus reduce the cost. However, such cageless type ball splines have a tendency of the balls to fall out of the body when assembled or disassembled, resulting in difficulties to check or repair. Another type ball splines are known which include a holder for guiding balls. However, they are disadvantageous in their poor ability to smoothly circulate the balls with a large ball rolling resistance due to the less radius of gyration of the balls running between load and unload regions and also in their difficulties encountered when assembled.